This invention relates to a process of manufacturing a semiconductor device, and more particularly to a process of manufacturing a semiconductor element or circuit using a transfer technique.
Bipolar transistors and MOS transistors formed on monocrystalline silicon surfaces show excellent electric characteristics and hence are used to constitute various types of electronic devices. Further, an SOI technique for forming a transistor on a thin silicon film, which film is formed on a silicon substrate with an insulating film interposed therebetween, has recently been developed to meet, for example, a demand for reduction of element size. In this technique, thermal oxidation, thermal diffusion, etc. are employed to form semiconductor elements. These heat treatments are usually performed at about 1000xc2x0 C.
On the other hand, semiconductor layers have come to be formed at a relatively low temperature by plasma CVD, laser crystallization, etc., on which layers are formed polycrystalline silicon thin film transistors or amorphous silicon thin film transistors.
At the present stage, there is a demand for application of the thin film transistors to a driving circuit incorporated in a wide-screen direct viewing display. To meet this demand, it is necessary to establish a big-scale substrate treatment technique.
The aforementioned process technique for forming silicon transistors is based on a heat treatment technique using a high temperature of about 1000xc2x0 C.
Therefore, a transistor of excellent electric characteristics, for example, cannot be formed on a semiconductor thin film provided on a substrate of a low heat resistance.
Although reduction of the process temperature has been realized by new techniques such as plasma CVD, laser crystallization, etc., it is still necessary, even in the case of using the new techniques, to set the process temperature at 300xc2x0 C. or more in order to form an element of excellent electric characteristics. Thus, it is difficult to directly form a transistor circuit on a non-heat-resistive substrate formed of, for example, plastic. In addition, in the case of directly forming transistor circuits on a large scale substrate, a large process apparatus is necessary, the precision of the process apparatus may well degrade, and produced transistor circuits will be expensive.
The present invention has been developed to solve the above problems, and is aimed at providing a process of forming a transistor circuit of excellent properties on a substrate of a low heat resistance, and realizing a large scale device.
The aim can be attained by the step of separating a film structure which consists of a single layer or plural layers and is necessary to form a transistor circuit, from a substrate which supports the film structure. If necessary, the film structure is adhered to another substrate of a low heat resistance. To this end, the invention employs a separation layer interposed between the film structure and the substrate supporting it.
In the process, according to the invention, of forming the film structure which consists of the single layer or plural layers and is necessary to form the transistor circuit, a separation layer is interposed beforehand between the substrate and the film structure.
After a transistor circuit, for example, is formed in the film structure by a high temperature treatment, the separation layer is removed by etching to separate the film structure from the support substrate.
In this case, the removal of the separation layer is more facilitated by forming air gaps in at least a portion of the layer.
In addition, in the invention, the step of separating the film structure from the support substrate by removing the separation layer can be performed during or after the formation of a desired semiconductor device in the film structure.
The semiconductor device circuit produced by the process of the invention is, for example, a circuit which consists of one or more thin film transistors, one or more MOSFETs, or one or more bipolar transistors, a circuit using a solar battery, or an integrated circuit consisting of a plurality of such active elements. It is a matter of course that the semiconductor device circuit is not limited to the above.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.